The present invention relates to a hot plate unit, and more particularly, to a hot plate unit for heating a silicon wafer during a semiconductor manufacturing process.
In a semiconductor manufacturing process, a hot plate unit is normally used to dry photosensitive resin, which is applied to silicon wafers. The hot plate unit is incorporated in a semiconductor manufacturing apparatus.
Japanese Examined Patent Publication 4-13873 describes a first example of a prior art hot plate unit. The hot plate unit includes a hot plate, which is made of an aluminum nitride sintered body, and a resistor arranged in the plate. The two ends of the resistor project from the sides of the plate and are connected to a power supply via wires.
A silicon wafer, which is the heating subject, is placed on the hot plate. When the resistor is supplied with current, the resistor is heated for a predetermined time period to heat the silicon wafer and dry the photosensitive resin. The flow of current is then stopped to gradually cool the hot plate and the silicon wafer. After the hot plate and the silicon wafer are cooled to a relatively low temperature, the silicon wafer is removed from the hot plate to undergo the next process. Since the time period for cooling the hot plate is relatively long, it is difficult to improve productivity.
To decrease the cooling time of the hot plate, the plate may be cooled by, for example, forcing cooling air against the lower surface of the hot plate. However, the moisture and dust in the forced air may contaminate the semiconductor manufacturing apparatus and its environment.
Japanese Examined Patent Publication No. 8-8246 describes a second example of a prior art hot plate. The hot plate includes a cooling body provided with cooling fins. However, although the cooling body cools the hot plate locally, the hot plate cannot be cooled entirely.
FIG. 1 shows a third example of a prior art hot plate unit 41. The hot plate unit 41 includes a cup-like casing 42 and a hot plate 43 made of a ceramic sintered body. The casing 42 is made of a metal material, such as aluminum, and has a lip 44 located at its upper portion. The casing 42 has an opening encompassed by the lip 44. Resistors 45 are arranged in a predetermined pattern at the lower surface of the hot plate 43. A plurality of screw holes 46 extend through the peripheral portion of the hot plate 43. A plurality of threaded holes 47 extend through the lip 44. The screw holes 46 of the hot plate 43 are aligned with the threaded holes 47 of the lip 44. A screw 48 is inserted into each set of aligned holes 46, 47 to fasten the hot plate 43 to the casing 42.
The hot plate unit 41 uses fasteners, such as the screws 48, to fasten the hot plate 43 directly to the metal casing 42. Thus, the heat of the hot plate 43 is transmitted to the casing 42 through the screws 48. As a result, the temperature at the periphery of the hot plate 43 tends to be lower. Furthermore, the hot plate 43 cannot be cooled in a uniform manner.
In addition, the fastening force of the screws 48 may damage the hot plate 43 since the force is applied directly to the hot plate 43. Further, it is difficult to machine threaded holes in the hot plate 43, which is made of a hard material.
Accordingly, it is a first object of the present invention to provide a hot plate unit that adjusts the temperature of a heating subject in a uniform manner. It is a second object of the present invention to provide a hot plate unit that is easily secured to a supporting body.
To achieve the above objects, the present invention provides a hot plate unit including a case and a hot plate having a heat generator. The case and the hot plate define a space in which a fluid flows.
Another aspect of the present invention provides a hot plate unit including a case having a lip, a hot plate having a heat generator, and a holder for securing the hot plate to the case. The hot plate is made of sintered ceramic. The holder contacts a peripheral portion of the upper surface of the hot plate when the holder is fixed to the case.
Further aspect of the present invention provides a hot plate unit including a case having a lip, a hot plate having a heat generator, and a seal element. The hot plate is made of sintered ceramic. The hot plate is secured to the case via the seal element. The seal element is heat insulative.
Further aspect of the present invention provides a hot plate unit including a case having a lip, a hot plate having a heat generator, and at least one intake port extending through the case.
Other aspects and advantages of the present invention will become apparent from the following description, taken in conjunction with the accompanying drawings, illustrating by way of example the principles of the invention.